Update EntityMut's location in push_children() and insert_children() (#2604)

## Objective

This code would result in a crash:
```rust
use bevy::prelude::*;

fn main() {
    let mut world = World::new();
    let child = world.spawn().id();
    world.spawn().push_children(&[child]);
}
```

## Solution

Update the `EntityMut`'s location after inserting a component on the children entities, as it may have changed.

Author: Davier

crates/bevy_transform/src/hierarchy/child_builder.rs

@@ -219,14 +219,16 @@ impl<'w> BuildWorldChildren for EntityMut<'w> {
     fn push_children(&mut self, children: &[Entity]) -> &mut Self {
         let parent = self.id();
         {
-            // SAFE: parent entity is not modified
+            // SAFE: parent entity is not modified and its location is updated manually
             let world = unsafe { self.world_mut() };
             for child in children.iter() {
                 world
                     .entity_mut(*child)
                     // FIXME: don't erase the previous parent (see #1545)
                     .insert_bundle((Parent(parent), PreviousParent(parent)));
             }
+            // Inserting a bundle in the children entities may change the parent entity's location if they were of the same archetype
+            self.update_location();
         }
         if let Some(mut children_component) = self.get_mut::<Children>() {
             children_component.0.extend(children.iter().cloned());
@@ -239,14 +241,16 @@ impl<'w> BuildWorldChildren for EntityMut<'w> {
     fn insert_children(&mut self, index: usize, children: &[Entity]) -> &mut Self {
         let parent = self.id();
         {
-            // SAFE: parent entity is not modified
+            // SAFE: parent entity is not modified and its location is updated manually
             let world = unsafe { self.world_mut() };
             for child in children.iter() {
                 world
                     .entity_mut(*child)
                     // FIXME: don't erase the previous parent (see #1545)
                     .insert_bundle((Parent(parent), PreviousParent(parent)));
             }
+            // Inserting a bundle in the children entities may change the parent entity's location if they were of the same archetype
+            self.update_location();
         }
 
         if let Some(mut children_component) = self.get_mut::<Children>() {
@@ -471,4 +475,11 @@ mod tests {
             PreviousParent(parent)
         );
     }
+
+    #[test]
+    fn regression_push_children_same_archetype() {
+        let mut world = World::new();
+        let child = world.spawn().id();
+        world.spawn().push_children(&[child]);
+    }
 }